Today is the anniversary of the Potsdam Declaration.
I highly recommend “Japan’s Decision to Surrender” by Robert Butow. He explores contemporaneous testimony on Japan’s leadership in those final days of WWII. Japan’s leadership, both civilian and military, wanted to keep their emperor; this conflicted directly with the demand for unconditional surrender and the elimination of all authority. Japan’s civilian leadership believed that this was possible if they surrendered to the UK (who had royalty) and the USA, but if they surrendered to the Soviet Union, that was it for the emperor.
While it my be true that continued bombardment of Japan with nuclear and conventional bombs would probably had eventually made it impossible for the country to continue to wage war, the two nuclear strikes did not do that, and the USA did not have additional nuclear bombs ready. Dropping conventional bombs also effectively destroyed military targets and started firestorms that caused massive infrastructure damage. Conventional strikes put more military personnel and resources at risk, but compared to a land assault, it may have been a less costly path. We’ll never know because the Soviets invaded Manchuria.
After reading Butow’s book, I think that the Soviet’s invasion of Manchuria was the breaking point. Not only did Japan lose a much needed resource that was feeding everyone in Japan, but it put the Soviet Union in close proximity. A land assault at this point would not have been just the western allies who were fighting in the Pacific; it would have included the Soviets who had just violated their non-aggression pact with Japan. So not only did the Soviets not keep their word with Japan, but the Soviets would most likely not allow Japan to keep their emperor.
And so, Japan chose to surrender to the UK and USA.
I don’t know how broadly distributed this interpretation was in the 1950s. However, I do know that the focus on nuclear weapons has been the dominant thread in more current interpretations. When I was a child, I learned the story as “We dropped one nuke; they didn’t surrender, so we dropped the second; they surrendered” which is chronologically true, but I think inaccurate.
As an adult, I’ve also heard the story that American casualties were expected to exceed 6 million for a land assault, which would have included my father and my husband’s father, but that begs the question of why not use conventional bombs to flatten Japan. Again, I think the nuclear weapon debate has taken this over: we had to use the nukes to avoid the massive casualties of a land assault. And, of course, both of these story lines are all about the USA and our choices, not about Japan and their choices at the end of WWII.